The present invention relates to an improved bearing assembly having primary, though not exclusive use, as a bearing assembly for steering columns for use in automotive vehicles, and to an elastomeric crown for use in such a bearing assembly.
A steering column includes all the elements necessary to enable motions of a steering wheel to be transmitted to a steering rack. The steering column includes a mounting tube in which a shaft, linking together the steering wheel and the steering rack, is guided in rotation. The shaft is supported in the tube by a plurality of bearing assemblies.
When used in steering columns, bearing assemblies must satisfy a number of conditions. Vehicle manufacturers specify the mounting, speed and temperature conditions at which the bearing assemblies will need to operate. The bearing assemblies must allow stresses from the steering wheel to be transmitted via the shaft and must run silently. Further, the bearing assemblies must maintain their properties throughout the working life of the steering column despite the various environmental factors encountered, including changing levels of temperature, humidity and grease.
It is known to construct bearing assemblies for this purpose comprising a split bearing, about which is located an elastic element, the elastic element in use being located between the bearing and a mounting tube to locate the bearing axially in relation to the mounting tube. In this way a continuous pressure may be maintained on the rear surface of the bearing acting to close the split.
However, in known bearing assemblies, such as those described above, the force exerted on the rear surface of the bearing will follow the intrinsic physical characteristics of the elastic element. In addition the force exerted will be affected by any irregularities on the inside surface of the housing. These characteristics can cause problems in obtaining and maintaining an even, or substantially even, force on the rear surface of the bearing. There is a need for an elastic element to have a substantially constant pressure on the rear surface of the bearing in order to guarantee the constancy of the rotating torque value. It would be an advantage for the substantially constant pressure to be at the minimum required to do this. This is because, unfortunately, in some circumstances, maintaining the substantially constant pressure on the rear surface of the bearing against the opposing force exerted by the bearing will cause creep bending to occur in the elastic element. Clearly, it would be an advantage to have the lowest stress level in the elastic element to avoid creep bending occurring.
It is an advantage of the present invention that an elastomeric crown according to the present invention eliminates or substantially reduces these problems.
According to a first aspect of the present invention, we provide an elastomeric crown for a bearing assembly comprising an elastomeric cylinder having an annular wall about a longitudinal axis, a plurality of passageways extending longitudinally through the cylinder wall and a plurality of ribs extending along an outer surface of the elastomeric cylinder.
Preferably the passageways extend parallel to the longitudinal axis of the elastomeric element.
The cross sectional shape of the passageways may be any desired and may include round, oval, hexagonal for example.
The elastomeric element is provided with a plurality of ribs extending along an outer surface of the elastomeric element.
More preferably the plurality of ribs extend substantially parallel to the longitudinal axis of the elastomeric cylinder.
More preferably the plurality of ribs are located radially of the passageways extending through the elastomeric element.
The cross sectional shape of the ribs may be any desired shape.
Preferably at least one of the plurality of ribs comprises a bead extending longitudinally along the elastomeric cylinder projecting from an outer surface of the elastomeric cylinder, the outer surface of the bead being a flat disposed parallel to a tangent of the outer surface of the elastomeric cylinder.
Preferably the plurality of passageways comprises twelve passageways.
According to a second aspect of the invention, we provide a bearing assembly comprising a cylindrical bearing having an axial split and an elastomeric crown according to the first aspect of the invention, the elastomeric crown being located about the split bearing.
Although the bearing assembly of the present invention is described with particular reference to steering columns for vehicles as an example of its use, the bearing assembly according to the present invention is effectively a xe2x80x9cclearance-free bearing assemblyxe2x80x9d where the bearing runs against a co-operating shaft without clearance due to the radially compressive force due to the crown. Thus, the bearing assembly of the present invention has many applications other than in steering columns.
According to a third aspect of the present invention, we provide a steering column assembly including at least one bearing assembly according to the second aspect of the invention.